1. Field of the Invention
The present invention relates to a noise elimination circuit of a matrix display device and a matrix display device using the noise elimination circuit, and in particular, to a noise elimination circuit included in a timing controller of a liquid crystal display device.
2. Description of the Related Art
In the related art, when a high voltage is applied to a casing body of a matrix display device, such as a liquid crystal display device, in a static noise test, for example, an abnormal display of the moment has been viewed. The abnormal display mainly occurs because a noise is introduced into an input terminal of the liquid crystal display device and the noise is superposed on a signal within a digital circuit included in a timing controller of the liquid crystal display device, and as a result, the timing controller malfunctions to output various control signals at timings different from those in a normal state.
Output signals of the timing controller mounted in the liquid crystal display device include a horizontal direction start pulse, a vertical direction start pulse, and the like, which are affected by the superposition of the static noise introduced into the input terminal. When the timing of the horizontal direction start pulse deviates, a line noise is generated, and when the horizontal direction start pulse is not output, the abnormal display, such as omission of a line, occurs. In addition, when the timing of the vertical direction start pulse deviates, the display rocking in the vertical direction occurs, and when the vertical direction start pulse is not output, the abnormal display, such as omission of a frame, occurs. The omission of a frame is not a big problem in a still image, while the omission of a frame causes a screen jump so as to make unnatural movements in a moving picture.
Further, in the case of an interface where horizontal and vertical synchronization signals are not included in a display control signal between the liquid crystal display device and a display controller controlling the liquid crystal display device, when a noise is superposed on a data enable signal (hereinafter, referred to as ‘DENA’) indicating the effective timing of display data, deformation of an image is noticeable, which has been a serious problem.
Furthermore, in an LVDS (low voltage differential signaling) interface widely used as an interface standard of the display control signal, when an operation voltage becomes less than a predetermined level, a receiving operation of an LVDS receiver becomes unstable, which causes malfunction so as to generate a noise signal.
A noise elimination circuit for preventing a digital circuit from malfunctioning when a noise is introduced thereinto has been proposed in which noise components of input signals are eliminated by preparing a plurality of input stages in consideration of a case where noises are included in the input signals and then comparing the input signals so as to determine the reliability of the signals (refer to JP-A-11-282401).
Further, there has been known a method in which a delay circuit is provided to a signal input stage and an input signal and a delayed input signal are combined so as to eliminate a noise (refer to JP-A-11-214964 and JP-A-11-251884).
Furthermore, there has been known a method in which a first filter circuit for a high frequency noise (narrow pulse width) and a second filter circuit for a low frequency noise (wide pulse width) are connected to each other so as to form a noise filter circuit (refer to JP-A-2000-341098).
In addition, a noise detection circuit for detecting noises, such as continuously generated noises or a noise having a wide pulse width (refer to JP-A-2000-209076).
In the noise elimination circuit disclosed in JP-A-11-282401, the sufficient performance cannot be obtained because, for example, noises cannot be filtered when the noises are introduced into all stages. In addition, in the noise elimination circuits disclosed in JP-A-11-214964 and JP-A-11-251884, in the case of a noise having a predefined pulse width or continuously generated noises, a noise of the input signal and a noise of the delayed input signal are superposed, and accordingly, the noise cannot be completely eliminated. In addition, in the noise elimination circuit disclosed in JP-A-2000-341098, since there is a limitation on the pulse width of a noise which can be eliminated, there is a possibility that an original signal will be removed when a noise having a wide pulse width is eliminated.
Further, in the noise detection circuit disclosed in JP-A-2000-209076, a level monitoring circuit for generating a level monitor signal for a predetermined period of time by detecting rising (or falling) edges of the input signal is provided so as to detect a noise during an operation period of the level monitoring circuit. However, in the noise detection circuit, even though a noise (Low) signal during an active (High) period can be detected, a noise (High) signal during an inactive (Low) period cannot be detected, and also, an additional noise elimination circuit is needed to obtain an original input signal because a noise elimination circuit is not provided.
Furthermore, in the noise elimination circuit disclosed in JP-A-2000-271427, an edge of the input signal is detected by using an edge detector, a timer that counts a predetermined period of time subsequent to the edge and a mask unit that masks the input signal while the timer counts are provided, and the input signal is masked, thereby eliminating noises. However, in the noise elimination circuit, even though a noise (Low) signal during an active (High) period can be detected, a noise (High) signal during an inactive (Low) period cannot be detected.
In addition, the active (High) period refers to a case in which the signal is a signal determining whether other input signals (for example, a data signal) are effective or not and the input signal is effective. The inactive (Low) period refers to a case in which the input signal is not effective. Hereinafter, definitions of the active and inactive periods are the same as described above.